diff --git a/mon/PGUtil.js b/mon/PGUtil.js
index c3512beb..d233d4b3 100644
--- a/mon/PGUtil.js
+++ b/mon/PGUtil.js
@@ -3,6 +3,7 @@
 
 module.exports = {
     scale_pg_count,
+    scale_pg_history,
 };
 
 function add_pg_history(new_pg_history, new_pg, prev_pgs, prev_pg_history, old_pg)
@@ -43,16 +44,18 @@ function finish_pg_history(merged_history)
     merged_history.all_peers = Object.values(merged_history.all_peers);
 }
 
-function scale_pg_count(prev_pgs, real_prev_pgs, prev_pg_history, new_pg_history, new_pg_count)
+function scale_pg_history(prev_pg_history, prev_pgs, new_pgs)
 {
-    const old_pg_count = real_prev_pgs.length;
+    const new_pg_history = [];
+    const old_pg_count = prev_pgs.length;
+    const new_pg_count = new_pgs.length;
     // Add all possibly intersecting PGs to the history of new PGs
     if (!(new_pg_count % old_pg_count))
     {
         // New PG count is a multiple of old PG count
         for (let i = 0; i < new_pg_count; i++)
         {
-            add_pg_history(new_pg_history, i, real_prev_pgs, prev_pg_history, i % old_pg_count);
+            add_pg_history(new_pg_history, i, prev_pgs, prev_pg_history, i % old_pg_count);
             finish_pg_history(new_pg_history[i]);
         }
     }
@@ -64,7 +67,7 @@ function scale_pg_count(prev_pgs, real_prev_pgs, prev_pg_history, new_pg_history
         {
             for (let j = 0; j < mul; j++)
             {
-                add_pg_history(new_pg_history, i, real_prev_pgs, prev_pg_history, i+j*new_pg_count);
+                add_pg_history(new_pg_history, i, prev_pgs, prev_pg_history, i+j*new_pg_count);
             }
             finish_pg_history(new_pg_history[i]);
         }
@@ -76,7 +79,7 @@ function scale_pg_count(prev_pgs, real_prev_pgs, prev_pg_history, new_pg_history
         let merged_history = {};
         for (let i = 0; i < old_pg_count; i++)
         {
-            add_pg_history(merged_history, 1, real_prev_pgs, prev_pg_history, i);
+            add_pg_history(merged_history, 1, prev_pgs, prev_pg_history, i);
         }
         finish_pg_history(merged_history[1]);
         for (let i = 0; i < new_pg_count; i++)
@@ -89,6 +92,12 @@ function scale_pg_count(prev_pgs, real_prev_pgs, prev_pg_history, new_pg_history
     {
         new_pg_history[i] = null;
     }
+    return new_pg_history;
+}
+
+function scale_pg_count(prev_pgs, new_pg_count)
+{
+    const old_pg_count = prev_pgs.length;
     // Just for the lp_solve optimizer - pick a "previous" PG for each "new" one
     if (prev_pgs.length < new_pg_count)
     {
diff --git a/mon/mon.js b/mon/mon.js
index 3a2a5fa9..a7ed66a6 100644
--- a/mon/mon.js
+++ b/mon/mon.js
@@ -59,6 +59,7 @@ const etcd_tree = {
             etcd_mon_timeout: 1000, // ms. min: 0
             etcd_mon_retries: 5, // min: 0
             mon_change_timeout: 1000, // ms. min: 100
+            mon_retry_change_timeout: 50, // ms. min: 10
             mon_stats_timeout: 1000, // ms. min: 100
             osd_out_time: 600, // seconds. min: 0
             placement_levels: { datacenter: 1, rack: 2, host: 3, osd: 4, ... },
@@ -498,6 +499,11 @@ class Mon
         {
             this.config.mon_change_timeout = 100;
         }
+        this.config.mon_retry_change_timeout = Number(this.config.mon_retry_change_timeout) || 50;
+        if (this.config.mon_retry_change_timeout < 50)
+        {
+            this.config.mon_retry_change_timeout = 50;
+        }
         this.config.mon_stats_timeout = Number(this.config.mon_stats_timeout) || 1000;
         if (this.config.mon_stats_timeout < 100)
         {
@@ -1230,6 +1236,89 @@ class Mon
         return aff_osds;
     }
 
+    async generate_pool_pgs(pool_id, osd_tree, levels)
+    {
+        const pool_cfg = this.state.config.pools[pool_id];
+        if (!this.validate_pool_cfg(pool_id, pool_cfg, false))
+        {
+            return null;
+        }
+        let pool_tree = osd_tree[pool_cfg.root_node || ''];
+        pool_tree = pool_tree ? pool_tree.children : [];
+        pool_tree = LPOptimizer.flatten_tree(pool_tree, levels, pool_cfg.failure_domain, 'osd');
+        this.filter_osds_by_tags(osd_tree, pool_tree, pool_cfg.osd_tags);
+        this.filter_osds_by_block_layout(
+            pool_tree,
+            pool_cfg.block_size || this.config.block_size || 131072,
+            pool_cfg.bitmap_granularity || this.config.bitmap_granularity || 4096,
+            pool_cfg.immediate_commit || this.config.immediate_commit || 'none'
+        );
+        // First try last_clean_pgs to minimize data movement
+        let prev_pgs = [];
+        for (const pg in ((this.state.history.last_clean_pgs.items||{})[pool_id]||{}))
+        {
+            prev_pgs[pg-1] = [ ...this.state.history.last_clean_pgs.items[pool_id][pg].osd_set ];
+        }
+        if (!prev_pgs.length)
+        {
+            // Fall back to config/pgs if it's empty
+            for (const pg in ((this.state.config.pgs.items||{})[pool_id]||{}))
+            {
+                prev_pgs[pg-1] = [ ...this.state.config.pgs.items[pool_id][pg].osd_set ];
+            }
+        }
+        const old_pg_count = prev_pgs.length;
+        const optimize_cfg = {
+            osd_tree: pool_tree,
+            pg_count: pool_cfg.pg_count,
+            pg_size: pool_cfg.pg_size,
+            pg_minsize: pool_cfg.pg_minsize,
+            max_combinations: pool_cfg.max_osd_combinations,
+            ordered: pool_cfg.scheme != 'replicated',
+        };
+        let optimize_result;
+        // Re-shuffle PGs if config/pgs.hash is empty
+        if (old_pg_count > 0 && this.state.config.pgs.hash)
+        {
+            if (prev_pgs.length != pool_cfg.pg_count)
+            {
+                // Scale PG count
+                // Do it even if old_pg_count is already equal to pool_cfg.pg_count,
+                // because last_clean_pgs may still contain the old number of PGs
+                PGUtil.scale_pg_count(prev_pgs, pool_cfg.pg_count);
+            }
+            for (const pg of prev_pgs)
+            {
+                while (pg.length < pool_cfg.pg_size)
+                {
+                    pg.push(0);
+                }
+            }
+            optimize_result = await LPOptimizer.optimize_change({
+                prev_pgs,
+                ...optimize_cfg,
+            });
+        }
+        else
+        {
+            optimize_result = await LPOptimizer.optimize_initial(optimize_cfg);
+        }
+        console.log(`Pool ${pool_id} (${pool_cfg.name || 'unnamed'}):`);
+        LPOptimizer.print_change_stats(optimize_result);
+        const pg_effsize = Math.min(pool_cfg.pg_size, Object.keys(pool_tree).length);
+        return {
+            pool_id,
+            pgs: optimize_result.int_pgs,
+            stats: {
+                total_raw_tb: optimize_result.space,
+                pg_real_size: pg_effsize || pool_cfg.pg_size,
+                raw_to_usable: (pg_effsize || pool_cfg.pg_size) / (pool_cfg.scheme === 'replicated'
+                    ? 1 : (pool_cfg.pg_size - (pool_cfg.parity_chunks||0))),
+                space_efficiency: optimize_result.space/(optimize_result.total_space||1),
+            },
+        };
+    }
+
     async recheck_pgs()
     {
         if (this.recheck_pgs_active)
@@ -1244,158 +1333,47 @@ class Mon
         const { up_osds, levels, osd_tree } = this.get_osd_tree();
         const tree_cfg = {
             osd_tree,
+            levels,
             pools: this.state.config.pools,
         };
         const tree_hash = sha1hex(stableStringify(tree_cfg));
         if (this.state.config.pgs.hash != tree_hash)
         {
             // Something has changed
-            const new_config_pgs = JSON.parse(JSON.stringify(this.state.config.pgs));
-            const etcd_request = { compare: [], success: [] };
-            for (const pool_id in (this.state.config.pgs||{}).items||{})
+            console.log('Pool configuration or OSD tree changed, re-optimizing');
+            // First re-optimize PGs, but don't look at history yet
+            const optimize_results = await Promise.all(Object.keys(this.state.config.pools)
+                .map(pool_id => this.generate_pool_pgs(pool_id, osd_tree, levels)));
+            // Then apply the modification in the form of an optimistic transaction,
+            // each time considering new pg/history modifications (OSDs modify it during rebalance)
+            while (!await this.apply_pool_pgs(optimize_results, up_osds, osd_tree, tree_hash))
             {
-                if (!this.state.config.pools[pool_id])
-                {
-                    // Pool deleted. Delete all PGs, but first stop them.
-                    if (!await this.stop_all_pgs(pool_id))
-                    {
-                        this.recheck_pgs_active = false;
-                        this.schedule_recheck();
-                        return;
-                    }
-                    const prev_pgs = [];
-                    for (const pg in this.state.config.pgs.items[pool_id]||{})
-                    {
-                        prev_pgs[pg-1] = this.state.config.pgs.items[pool_id][pg].osd_set;
-                    }
-                    // Also delete pool statistics
-                    etcd_request.success.push({ requestDeleteRange: {
-                        key: b64(this.etcd_prefix+'/pool/stats/'+pool_id),
-                    } });
-                    this.save_new_pgs_txn(new_config_pgs, etcd_request, pool_id, up_osds, osd_tree, prev_pgs, [], []);
-                }
-            }
-            for (const pool_id in this.state.config.pools)
-            {
-                const pool_cfg = this.state.config.pools[pool_id];
-                if (!this.validate_pool_cfg(pool_id, pool_cfg, false))
-                {
-                    continue;
-                }
-                let pool_tree = osd_tree[pool_cfg.root_node || ''];
-                pool_tree = pool_tree ? pool_tree.children : [];
-                pool_tree = LPOptimizer.flatten_tree(pool_tree, levels, pool_cfg.failure_domain, 'osd');
-                this.filter_osds_by_tags(osd_tree, pool_tree, pool_cfg.osd_tags);
-                this.filter_osds_by_block_layout(
-                    pool_tree,
-                    pool_cfg.block_size || this.config.block_size || 131072,
-                    pool_cfg.bitmap_granularity || this.config.bitmap_granularity || 4096,
-                    pool_cfg.immediate_commit || this.config.immediate_commit || 'none'
+                console.log(
+                    'Someone changed PG configuration while we also tried to change it.'+
+                    ' Retrying in '+this.config.mon_retry_change_timeout+' ms'
                 );
-                // These are for the purpose of building history.osd_sets
-                const real_prev_pgs = [];
-                let pg_history = [];
-                for (const pg in ((this.state.config.pgs.items||{})[pool_id]||{}))
+                // Failed to apply - parallel change detected. Wait a bit and retry
+                const old_rev = this.etcd_watch_revision;
+                while (this.etcd_watch_revision === old_rev)
                 {
-                    real_prev_pgs[pg-1] = this.state.config.pgs.items[pool_id][pg].osd_set;
-                    if (this.state.pg.history[pool_id] &&
-                        this.state.pg.history[pool_id][pg])
-                    {
-                        pg_history[pg-1] = this.state.pg.history[pool_id][pg];
-                    }
+                    await new Promise(ok => setTimeout(ok, this.config.mon_retry_change_timeout));
                 }
-                // And these are for the purpose of minimizing data movement
-                let prev_pgs = [];
-                for (const pg in ((this.state.history.last_clean_pgs.items||{})[pool_id]||{}))
-                {
-                    prev_pgs[pg-1] = this.state.history.last_clean_pgs.items[pool_id][pg].osd_set;
-                }
-                prev_pgs = JSON.parse(JSON.stringify(prev_pgs.length ? prev_pgs : real_prev_pgs));
-                const old_pg_count = real_prev_pgs.length;
-                const optimize_cfg = {
-                    osd_tree: pool_tree,
-                    pg_count: pool_cfg.pg_count,
-                    pg_size: pool_cfg.pg_size,
-                    pg_minsize: pool_cfg.pg_minsize,
-                    max_combinations: pool_cfg.max_osd_combinations,
-                    ordered: pool_cfg.scheme != 'replicated',
+                const new_ot = this.get_osd_tree();
+                const new_tcfg = {
+                    osd_tree: new_ot.osd_tree,
+                    levels: new_ot.levels,
+                    pools: this.state.config.pools,
                 };
-                let optimize_result;
-                if (old_pg_count > 0)
+                if (sha1hex(stableStringify(new_tcfg)) !== tree_hash)
                 {
-                    if (old_pg_count != pool_cfg.pg_count)
-                    {
-                        // PG count changed. Need to bring all PGs down.
-                        if (!await this.stop_all_pgs(pool_id))
-                        {
-                            this.recheck_pgs_active = false;
-                            this.schedule_recheck();
-                            return;
-                        }
-                    }
-                    if (prev_pgs.length != pool_cfg.pg_count)
-                    {
-                        // Scale PG count
-                        // Do it even if old_pg_count is already equal to pool_cfg.pg_count,
-                        // because last_clean_pgs may still contain the old number of PGs
-                        const new_pg_history = [];
-                        PGUtil.scale_pg_count(prev_pgs, real_prev_pgs, pg_history, new_pg_history, pool_cfg.pg_count);
-                        pg_history = new_pg_history;
-                    }
-                    for (const pg of prev_pgs)
-                    {
-                        while (pg.length < pool_cfg.pg_size)
-                        {
-                            pg.push(0);
-                        }
-                    }
-                    if (!this.state.config.pgs.hash)
-                    {
-                        // Re-shuffle PGs
-                        optimize_result = await LPOptimizer.optimize_initial(optimize_cfg);
-                    }
-                    else
-                    {
-                        optimize_result = await LPOptimizer.optimize_change({
-                            prev_pgs,
-                            ...optimize_cfg,
-                        });
-                    }
+                    // Configuration actually changed, restart from the beginning
+                    this.recheck_pgs_active = false;
+                    setImmediate(() => this.recheck_pgs().catch(this.die));
+                    return;
                 }
-                else
-                {
-                    optimize_result = await LPOptimizer.optimize_initial(optimize_cfg);
-                }
-                if (old_pg_count != optimize_result.int_pgs.length)
-                {
-                    console.log(
-                        `PG count for pool ${pool_id} (${pool_cfg.name || 'unnamed'})`+
-                        ` changed from: ${old_pg_count} to ${optimize_result.int_pgs.length}`
-                    );
-                    // Drop stats
-                    etcd_request.success.push({ requestDeleteRange: {
-                        key: b64(this.etcd_prefix+'/pg/stats/'+pool_id+'/'),
-                        range_end: b64(this.etcd_prefix+'/pg/stats/'+pool_id+'0'),
-                    } });
-                }
-                LPOptimizer.print_change_stats(optimize_result);
-                const pg_effsize = Math.min(pool_cfg.pg_size, Object.keys(pool_tree).length);
-                this.state.pool.stats[pool_id] = {
-                    used_raw_tb: (this.state.pool.stats[pool_id]||{}).used_raw_tb || 0,
-                    total_raw_tb: optimize_result.space,
-                    pg_real_size: pg_effsize || pool_cfg.pg_size,
-                    raw_to_usable: (pg_effsize || pool_cfg.pg_size) / (pool_cfg.scheme === 'replicated'
-                        ? 1 : (pool_cfg.pg_size - (pool_cfg.parity_chunks||0))),
-                    space_efficiency: optimize_result.space/(optimize_result.total_space||1),
-                };
-                etcd_request.success.push({ requestPut: {
-                    key: b64(this.etcd_prefix+'/pool/stats/'+pool_id),
-                    value: b64(JSON.stringify(this.state.pool.stats[pool_id])),
-                } });
-                this.save_new_pgs_txn(new_config_pgs, etcd_request, pool_id, up_osds, osd_tree, real_prev_pgs, optimize_result.int_pgs, pg_history);
+                // Configuration didn't change, PG history probably changed, so just retry
             }
-            new_config_pgs.hash = tree_hash;
-            await this.save_pg_config(new_config_pgs, etcd_request);
+            console.log('PG configuration successfully changed');
         }
         else
         {
@@ -1442,8 +1420,81 @@ class Mon
         this.recheck_pgs_active = false;
     }
 
-    async save_pg_config(new_config_pgs, etcd_request = { compare: [], success: [] })
+    async apply_pool_pgs(results, up_osds, osd_tree, tree_hash)
     {
+        for (const pool_id in (this.state.config.pgs||{}).items||{})
+        {
+            // We should stop all PGs when deleting a pool or changing its PG count
+            if (!this.state.config.pools[pool_id] ||
+                this.state.config.pgs.items[pool_id] && this.state.config.pools[pool_id].pg_count !=
+                Object.keys(this.state.config.pgs.items[pool_id]).reduce((a, c) => (a < (0|c) ? (0|c) : a), 0))
+            {
+                if (!await this.stop_all_pgs(pool_id))
+                {
+                    return false;
+                }
+            }
+        }
+        const new_config_pgs = JSON.parse(JSON.stringify(this.state.config.pgs));
+        const etcd_request = { compare: [], success: [] };
+        for (const pool_id in (new_config_pgs||{}).items||{})
+        {
+            if (!this.state.config.pools[pool_id])
+            {
+                const prev_pgs = [];
+                for (const pg in new_config_pgs.items[pool_id]||{})
+                {
+                    prev_pgs[pg-1] = new_config_pgs.items[pool_id][pg].osd_set;
+                }
+                // Also delete pool statistics
+                etcd_request.success.push({ requestDeleteRange: {
+                    key: b64(this.etcd_prefix+'/pool/stats/'+pool_id),
+                } });
+                this.save_new_pgs_txn(new_config_pgs, etcd_request, pool_id, up_osds, osd_tree, prev_pgs, [], []);
+            }
+        }
+        for (const pool_res of results)
+        {
+            const pool_id = pool_res.pool_id;
+            const pool_cfg = this.state.config.pools[pool_id];
+            let pg_history = [];
+            for (const pg in ((this.state.config.pgs.items||{})[pool_id]||{}))
+            {
+                if (this.state.pg.history[pool_id] &&
+                    this.state.pg.history[pool_id][pg])
+                {
+                    pg_history[pg-1] = this.state.pg.history[pool_id][pg];
+                }
+            }
+            const real_prev_pgs = [];
+            for (const pg in ((this.state.config.pgs.items||{})[pool_id]||{}))
+            {
+                real_prev_pgs[pg-1] = [ ...this.state.config.pgs.items[pool_id][pg].osd_set ];
+            }
+            if (real_prev_pgs.length > 0 && real_prev_pgs.length != pool_res.pgs.length)
+            {
+                console.log(
+                    `Changing PG count for pool ${pool_id} (${pool_cfg.name || 'unnamed'})`+
+                    ` from: ${real_prev_pgs.length} to ${pool_res.pgs.length}`
+                );
+                pg_history = PGUtil.scale_pg_history(pg_history, real_prev_pgs, pool_res.pgs);
+                // Drop stats
+                etcd_request.success.push({ requestDeleteRange: {
+                    key: b64(this.etcd_prefix+'/pg/stats/'+pool_id+'/'),
+                    range_end: b64(this.etcd_prefix+'/pg/stats/'+pool_id+'0'),
+                } });
+            }
+            const stats = {
+                used_raw_tb: (this.state.pool.stats[pool_id]||{}).used_raw_tb || 0,
+                ...pool_res.stats,
+            };
+            etcd_request.success.push({ requestPut: {
+                key: b64(this.etcd_prefix+'/pool/stats/'+pool_id),
+                value: b64(JSON.stringify(stats)),
+            } });
+            this.save_new_pgs_txn(new_config_pgs, etcd_request, pool_id, up_osds, osd_tree, real_prev_pgs, pool_res.pgs, pg_history);
+        }
+        new_config_pgs.hash = tree_hash;
         etcd_request.compare.push(
             { key: b64(this.etcd_prefix+'/mon/master'), target: 'LEASE', lease: ''+this.etcd_lease_id },
             { key: b64(this.etcd_prefix+'/config/pgs'), target: 'MOD', mod_revision: ''+this.etcd_watch_revision, result: 'LESS' },
@@ -1451,14 +1502,8 @@ class Mon
         etcd_request.success.push(
             { requestPut: { key: b64(this.etcd_prefix+'/config/pgs'), value: b64(JSON.stringify(new_config_pgs)) } },
         );
-        const res = await this.etcd_call('/kv/txn', etcd_request, this.config.etcd_mon_timeout, 0);
-        if (!res.succeeded)
-        {
-            console.log('Someone changed PG configuration while we also tried to change it. Retrying in '+this.config.mon_change_timeout+' ms');
-            this.schedule_recheck();
-            return;
-        }
-        console.log('PG configuration successfully changed');
+        const txn_res = await this.etcd_call('/kv/txn', etcd_request, this.config.etcd_mon_timeout, 0);
+        return txn_res.succeeded;
     }
 
     // Schedule next recheck at least at <unixtime>
diff --git a/tests/run_3osds.sh b/tests/run_3osds.sh
index affa6fa9..eb243aa3 100644
--- a/tests/run_3osds.sh
+++ b/tests/run_3osds.sh
@@ -53,7 +53,7 @@ for i in $(seq 1 $OSD_COUNT); do
     start_osd $i
 done
 
-(while true; do node mon/mon-main.js --etcd_url $ETCD_URL --etcd_prefix "/vitastor" --verbose 1 || true; done) &>./testdata/mon.log &
+(while true; do node mon/mon-main.js --etcd_address $ETCD_URL --etcd_prefix "/vitastor" --verbose 1 || true; done) >>./testdata/mon.log 2>&1 &
 MON_PID=$!
 
 if [ "$SCHEME" = "ec" ]; then
diff --git a/tests/test_change_pg_count.sh b/tests/test_change_pg_count.sh
index 5492983c..2a1ce213 100755
--- a/tests/test_change_pg_count.sh
+++ b/tests/test_change_pg_count.sh
@@ -18,6 +18,7 @@ try_change()
     for i in {1..6}; do
         echo --- Change PG count to $n --- >>testdata/osd$i.log
     done
+    echo --- Change PG count to $n --- >>testdata/mon.log
 
     $ETCDCTL put /vitastor/config/pools '{"1":{'$POOLCFG',"pg_size":'$PG_SIZE',"pg_minsize":'$PG_MINSIZE',"pg_count":'$n'}}'
 
diff --git a/tests/test_failure_domain.sh b/tests/test_failure_domain.sh
index 99f58c4a..8296bbf1 100755
--- a/tests/test_failure_domain.sh
+++ b/tests/test_failure_domain.sh
@@ -15,7 +15,7 @@ $ETCDCTL put /vitastor/osd/stats/7 '{"host":"host4","size":1073741824,"time":"'$
 $ETCDCTL put /vitastor/osd/stats/8 '{"host":"host4","size":1073741824,"time":"'$TIME'"}'
 $ETCDCTL put /vitastor/config/pools '{"1":{"name":"testpool","scheme":"replicated","pg_size":2,"pg_minsize":1,"pg_count":4,"failure_domain":"rack"}}'
 
-node mon/mon-main.js --etcd_url $ETCD_URL --etcd_prefix "/vitastor" &>./testdata/mon.log &
+node mon/mon-main.js --etcd_address $ETCD_URL --etcd_prefix "/vitastor" >>./testdata/mon.log 2>&1 &
 MON_PID=$!
 
 sleep 2
diff --git a/tests/test_vm_cont.sh b/tests/test_vm_cont.sh
index 2116cd31..fb778c43 100755
--- a/tests/test_vm_cont.sh
+++ b/tests/test_vm_cont.sh
@@ -15,7 +15,7 @@ for i in $(seq 1 $OSD_COUNT); do
     eval OSD${i}_PID=$!
 done
 
-(while true; do node mon/mon-main.js --etcd_url $ETCD_URL --etcd_prefix "/vitastor" --verbose 1 || true; done) &>./testdata/mon.log &
+(while true; do node mon/mon-main.js --etcd_address $ETCD_URL --etcd_prefix "/vitastor" --verbose 1 || true; done) >>./testdata/mon.log 2>&1 &
 MON_PID=$!
 
 sleep 3